1. Field of the Invention
This invention relates to photoresists particularly suitable for deep U.V. exposure and having the capability of forming highly resolved features of submicron dimensions.
2. Background Art
Photoresists are photosensitive films used for transfer of images to a substrate. They form negative or positive images. After a coating of a photoresist is formed on a substrate, the coating is selectively exposed through a photomask to a source of activating energy such as ultraviolet light. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. The pattern in the photomask of opaque and transparent areas defines a desired image to be transferred to a substrate. A relief image is provided upon development of the latent image patterned in the resist coating. The use of photoresists are generally described, for example, in Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York (1975), and in Moreau, Semiconductor Lithography, Principles, Practices and Materials, Plenum Press, New York (1988).
Known photoresists can form features having resolution and size sufficient for many commercial applications. However for many other applications the need exists for new photoresists that can provide highly resolved images of submicron dimensions.
In U.S. Pat. No. 5,128,232 to Thackeray et al. highly useful photoresist compositions are disclosed. The patent discloses, inter alia, use of a resist resin binder that comprises a copolymer of nonaromatic cyclic alcohol and phenol units. The disclosed photoresists are particularly suitable for exposure by deep U.V. radiation. As is recognized by those in the art "deep U.V. radiation" refers to exposure radiation having a wavelength in the range of about 350 nm or less, more typically in the range of about 300 nm or less.